Marine Mammals:Part 1

Marine Vertebrates: Lecture 7

Notochord; Dorsal, hollow nerve tube; pharynx with slits, post-anal tail (with segmented muscle bands)

Cranium formed from neural crest cells

Plus paired appendages (2 pair)

Class Mammalia: Key characteristics

Mammary glands (milk production) Hair Endothermic Efficient circulatory system (4-chambered

heart) Efficient respiratory system (diaphragm) Internal fertilization Relatively large brains Differentiation of teeth Development of malleus and incus in

middle ear (reptiles already have stapes)

Order Carnivora• Ursidae: polar bears• Mustilidae: sea otters

(Sub)order Pinnipedia• Phocidae• Otariidae• Odobenidae

Order Sirenia

•Manatees and dugongs

Order Cetacea• Suborder Odontoceti• Suborder Mysticeti

Osmotic balance

• Acquiring water Diet Drink Metabolically-produced water

• Water loss Skin, sweat glands, exhalation

• Excretion of water and ions Kidneys

• Concentrating ability mirrors reptile/bird salt glands

Thermoregulation

• Heat retention: Fur vs. blubber Dry fur is a more efficient insulator than blubber Specializations of marine mammal fur

• Fur seals and sea otters

• Polar bears

• Regulation of heat via blood flow changes Regulating flow to capillary beds

• Esp. hairless regions of body Countercurrent exchange

• Large size and shape Surface to volume low… Comparison to land mammals

Order CarnivoraFamily Ursidae

Adaptations to marine existence

• Streamlining No prominent shoulder humps Small head; small ears

• Adaptations for swimming Paws are larger, partly webbed Also allows for more even distribution of

weight on ice Long neck (how of value?) Dog paddle!

• Thermoregulation Thicker fur Clear, hollow guard hairs These may actually absorb ultraviolet light) >2x the size of grizzlies (up to 1800

pounds)

Habitat/Feeding ecology• Circumpolar distribution

Stable, but not continuous, (mostly) annual pack ice Can’t find prey without

• Seal specialists; will also hunt other marine mammals

Follow leads or finding holes made by their prey.

• Male vs. female foraging Males venture further out onto less-stable pack ice

• Avoid the most unstable ice near the ice edge ideal pupping grounds for seals

Females remain on more-stable pack ice closer to den sites.

• Locate ringed seal pups in dens beneath snow or in small ice caves in the pack ice

Use their sense of smell

Life History• Mating

April/May ~3:1 Male:Female

“operational sex ratio” (Why?)

Induced ovulation: Delayed implantation

• Maternity dens (~ mid-October)

• Young born in December/January Young are 1-1.5 pounds at birth!

Usually two.• Break out of dens (~

March/April) Young ~25-30 pounds Female is hungry…

• Cubs with mother for 2.5 years

Conservation status: Threatened

• Key threats Habitat loss

• Global climate change

Harvesting Water pollution

Order CarnivoraFamily Mustilidae: sea otters!

Overview/adaptations to marine

existence• Size: quite small for a marine mammal

45-65 pounds

• Dive stats: 120 feet; 4 minutes breath-hold• Thermoregulation (water is 30-50F)

Fur High metabolic rate (25% of body weight per day)

• Swim on their backs• Use webbed hindflippers in an alternate

motion for propulsion; also use their flattened tail.

Relatively slow for marine mammals, ~2-3 kt cruising speed.

• Forelimbs are very mobile, resemble arms and hands for collecting/manipulating food

Habitat/feeding ecology

• Live in kelp forests Wrap themselves and their young in the kelp...

• Feed on a wide variety of benthic invertebrates

sea urchins, abalone, crabs, sea stars, clams, scallops, etc…

May play important role in maintenance of kelp beds

• Tool users (bang creatures with exoskeletons, shells, and even endoskeletons on rocks)

• Kelp itself provides some protection from predation.

Sea otter: Historic distribution

Sea otter: Current distribution

Conservation status: Endangered

CA sea otter population: steady, some slow growth

AK (Aleutian Islands) huge decline• Orca predation

Major threats• Coastal pollution

• Oil spills

• Cat litter and Toxoplasma gondii

• Decline of other marine mammals…